Rentals can be a nice profit contributor to your business - two keys are unit utlization (based on $ potetnional ) and cost controls (internal cost & customer cost primarily documenting & charging for abuse, over time usage, etc. Don't jump into it unless you are prepared finanically, orgaizationally ready to support rental activity.
Rental are great "paid for demos".
Do some research, talk to dealers in the busness in your area about rentals, rates & rental management, agreements etc. first and see if this is "up your alley"